Rotary magnetron magnet bar and apparatus containing the same for high target utilization

ABSTRACT

An apparatus for coating a substrate is provided that includes a racetrack-shaped plasma source having two straight portions and at least one terminal turnaround portion connecting said straight portions. A tubular target formed of a target material that forms a component of the coating has an end. The target is in proximity to the plasma source for sputtering of the target material. The target is secured to a tubular backing cathode, with both being rotatable about a central axis. A set of magnets are arranged inside the cathode to move an erosion zone aligned with the terminal turnaround toward the end of the target as the target is utilized to deposit the coating on the substrate. Target utilization of up to 87 weight percent the initial target weight is achieved.

RELATED APPLICATIONS

This application claims priority benefit of U.S. Provisional ApplicationSer. No. 61/254,983 filed 26 Oct. 2009; the contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates in general to rotary sputter magnetronsalso called cylindrical magnetrons and in particular to improving thetarget utilization of these devices.

BACKGROUND

Rotary magnetron sputtering is well known in the art following McKelvey,AS EVIDENCED BY U.S. Pat. No. 4,446,877. FIGS. 1A, 1B, 2A, and 2B show aconventional, prior art rotary magnetron with a sputter racetrack 2proximal to the outer surface of the target tube cylinder 1. the targetcylinder 1 is supported on a backing tube 14. The sputter racetrack 2generates a plasma region proximal to the target material 10 to induceremoval of target material 10 and onto a deposition substrate. As isknown, the sputter target material 10 is formed into a target cylinder 1and the cylinder 1 is rotated on spindle 6 while an internal magnet bar20 is held stationary within the cylinder 2, as shown in FIG. 2A. Theresult is a sputter magnetron racetrack 2 of deposition plasma appearson the rotating tube during operation, as best seen in FIG. 1A that is amagnified longitudinal cross sectional view of region IB of FIG. 1A. Theracetrack 2 has linear portions 4 and turnaround portions 3. Theapproximate registry is shown between an interior edge 5 of turnaroundportion 3 and the point of maximal target wear 7 and is a result of thedifferences in plasma density and magnetic electron confinement to whichthe target material is exposed proximal to turnaround portion 3 relativeto linear portions 4. As will be detailed subsequently, the magneticfield generated by the magnet bar is also important in establishing thepoint of maximal erosion 7. It is appreciated that the opposing end ofthe target cylinder 1 has a mirror image erosion zone to that shown inthe accompanying figures associated with the other end of the racetrack2. This mirror image zone is not shown for visual clarity yet isotherwise identical in formation and shape to that depicted.

As is known, while considerably better than planar magnetron sputtering,target utilization is only approximately 60% for a typical rotarymagnetron. The reason for this is premature target wear of the cylinder1 in the vicinity of the turnaround 3 of the sputter racetrack 2. Thisis shown with greater clarity in the FIG. 1B cross-section view. Thetarget cylinder 1 before usage has a surface 15 that defined an initialtarget thickness. As target tube material 10 is sputtered off the targetcylinder 1, the cylinder section 13 proximal to the turnaround portion 3of the racetrack 2 wears faster than the cylinder section 12 proximal toa straightway portion of the racetrack 2. The operational lifetime of atarget tube cylinder 1 is exhausted when the target material is wornthrough almost to backing tube 14. Sputtering of the backing tube 14onto the substrate contaminates the deposited film. Due to the fasterwear, this occurs at a cylinder section 13 first, leaving considerabletarget material 10 unusable along straight away section 12 underlyingstraight portion 4. A conventional solution to this detrimentalturnaround wear pattern is the usage of a target with added thickness inthe end regions and underlying the turnaround portions 3. Such targetsare commonly referred to as “dog-boned”. While the thicker dog-bonedregion improves target utilization, this comes are the cost of morecomplicated target formation and a larger overall target diameter to thetarget. The increased separation distance between the target surface anda substrate for coating increases magnetron energy consumption andoverall efficiency.

FIG. 2A shows a more detailed longitudinal cross-sectional view proximalto the turnaround portion 3 of a conventional, prior art rotarymagnetron racetrack 2 along line of FIG. 1A. The backing tube 14 isshown in partial cutaway for visual clarity. In this cross-sectionalview the internal, stationary magnet bar 20 is shown positioned proximalto rotating backing tube 14 and target material 10. A correspondingtransverse cross sectional perspective view is shown in FIG. 2B that istaken along line IIB-IIB of FIG. 1A. The internal magnet bar 20 has amagnetic shunt 26 and magnets 27 and 28. The arrows depict the magneticpolarity according to common convention with the arrowhead pointingtowards a north pole. The configuration of magnets 27 and 28 and shunt26 result in magnetic field lines 30 that arch over and through targetmaterial 10. The apex of the field lines arching over and through thetarget is plotted as field line 29. Since, as is known, electrons tendto have concentrated density at the center of the arch, the principalerosion region of cylinder section 13 coincides with along field line 29when racetrack 2 is generating plasma. This plasma being concentrated inthe turnaround portion 3 relative to straight portion 4. In this case,field line 29 is roughly normal to the surface of the cylinder 1. Theerosion zone at the at the cylinder portion 13 then is continuouslyfocused over the same linear location at point 7 on the target tube andexcessive wear occurs as shown by the worn target profile of cylindersection 13. As shown, the cylinder section 13 is worn to the backingtube 14 at point 7 while substantial target material remains unusedalong straightaway cylinder section 12, underlying straight portion 4.

Prior art attempts have been made to improve target utilization have metwith limited success. One such prior art configuration is depicted inFIG. 3 and teaches away from the present invention. Like numerals usedin FIG. 3 have the meaning ascribed thereto with respect to thepreceding figures. FIG. 3 shows a cross-sectional view of U.S. Pat. No.5,364,518. In this patent, the problem of poor target utilization ofrotary magnetrons is recognized and the attempts to improve targetutilization. FIG. 3 is based on FIG. 7B of U.S. Pat. No. 5,364,518 andthe resulting target erosion profile is shown overlaid on this drawing,where a magnetic shunt 120 is added to the side of magnet 107 and shunt106 to pull magnetic flux toward the end 125 of target tube cylinder 1.This is taught in U.S. Pat. No. 5,364,518 to widen the target erosionregion at the turnaround region 13 and improves target utilization. Ananalysis of the proposed solution shows the apex of the resultingmagnetic field lines 130 plotted as line 109. As shown, line 109 is offnormal line 131 by angle θ, also referenced as 110. This geometryresults in the erosion zone 114 starting out closer to the end of targetcylinder 1. As the target cylinder 1 is eroded, the erosion zone followsline 109 and moves away from the end 125 of the target cylinder 1.Unfortunately, this has only a minimal benefit to overall targetutilization. By moving the erosion zone 114 progressively toward thestraight away section of cylinder 1 and underlying straight portion 4 ofracetrack 2 with continued removal of target material 10, the erosionzone moves toward a high erosion region of the target and merelybroadens the width of the erosion zone relative to that of FIGS. 1B and2A.

This broadening is understood with reference to the following equationthat approximates the terminal target cross section, t(l) when nofurther target sputtering can occur without risk of backing tubesputtering:

t(l)=D _(r)(1−e ^(k(l−l)) _(f))²  (I)

where D_(f) is the final erosion depth and roughly models the width ofthe erosion zone with a smaller value of D_(f) corresponding to a widererosion zone, l is the lateral position and l_(f) is the maximal erosionpoint denoted at 7 in the aforementioned drawings, and k is a fittingconstant.

The approximate fit of equation (I) onto a conventional erosion profileof FIG. 2A is shown graphically as a dashed line in FIG. 2C. For anoimalized erosion profile where the initial target thickness is aunitless value of 1 and point 7 is at l=1, the depicted fit correspondsto two parameter fit for D_(f)=0.48 and l_(f)=0.88, where k=1. It isappreciated that the erosion profile of FIG. 3 is similarly fit withthis expression with a best two parameter for D_(f)=0.40 and l_(f)=0.96,where k=1.

Thus, there exists a need for a magnet bar and an apparatus includingthe same that provides more efficient target utilization for rotarymagnetrons. There further exists a need for moving the erosion zone awayfrom the straightaway region of a proximal racetrack to afford animprovement in target utilization.

SUMMARY OF THE INVENTION

An apparatus for coating a substrate is provided that includes aracetrack-shaped plasma source having two straight portions and at leastone terminal turnaround portion connecting said straight portions. Atubular target formed of a target material that forms a component of thecoating has an end. The target is in proximity to the plasma source forsputtering of the target material. The target is secured to a tubularbacking cathode, with both being rotatable about a central axis. A setof magnets are arranged inside the cathode to move an erosion zonealigned with the terminal turnaround toward the end of the target as thetarget is utilized to deposit the coating on the substrate. Targetutilization of up to 87 weight percent the initial target weight isachieved.

A process of coating a substrate includes energizing a tubular targetunder conditions to generate a sputtering racetrack-shaped plasmaextending towards the substrate. The target is formed of a tube materialand has a tube end and is affixed to a tubular cathode that forms a tubebacking Magnets inside the cathode create a magnetic field whichinteracts with a racetrack-shaped plasma source aligned with the target.The plasma source has two straight portions and at least one terminalturnaround portion connecting the straight portions to move an erosionzone on the tubular target toward the end of the target as the target isutilized to deposit the coating on the substrate. The tube end beingaligned with at the least one terminal turnaround of the plasma source.A spent rotary magnetron target is thereby produced having astraightaway portion that intersects the end at said erosion zone at anangle β of between 70 and 90 degrees and has lost between 70 and 87weight percent the initial weight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a prior art perspective view of a conventional sputterracetrack on the outside of a rotary magnetron;

FIG. 1B shows a prior art longitudinal cross sectional magnified view oftarget tube erosion profile at the racetrack turnaround rotary magnetronof region IB along line of FIG. 1A;

FIG. 2A shows a more detailed prior art longitudinal cross sectionalview magnified view of target tube erosion profile at the racetrackturnaround rotary magnetron of region IB along line IIA-IIA of FIG. 1Ainclusive of the magnetron magnet bar and depicting the field lineoverlap with the resulting target tube erosion profile;

FIG. 2B shows a prior art perspective transverse cross sectional viewalong line IIB-IIB of FIG. 1A;

FIG. 2C shows a curve fit of Equation (I) to the erosion zone profile ofFIG. 1B;

FIG. 3 shows a prior art longitudinal cross sectional view of a a targettube erosion profile for U.S. Pat. No. 5,364,518, FIG. 7B that attemptsto limit localized target thinning as shown in the preceding figures;

FIG. 4 shows a longitudinal cross sectional view of the racetrackturnaround region of the target and an arrangement of an inventivestationary internal bar magnet with the resulting target profile as afunction of time;

FIG. 5A shows a longitudinal cross sectional view the prior art targetutilization terminal profile (dashed) as an overlay of the inventivetarget utilization terminal profile; and

FIG. 5B shows normalized plots of the prior art and inventive targetutilization of FIG. 5A with fits thereto using equation (I).

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention has utility as rotary magnetron with higher weightpercentage target utilization than has been heretofor obtainable. Thisis achieved by changing the magnetic field apex as a function ofoperational time from a position over the original target surface sothat as the target tube erodes, the magnetic field apex shifts towardthe end of the target cylinder thereby shifting the target erosion zoneoutward toward the end of the target tube to form a more stepped andoutwardly shifted erosion zone. The present invention is premised on therealization that the target tube material at the end of the targetcylinder more efficiently uses tube material compared to the prior art.By shifting the erosion zone toward the end of the target tube cylinderthrough the inclusion of an intermediate magnet with a polaritydifferent than that of the distal magnet of a magnet bar assemblyadjacent thereto, the tube cylinder zones of maximal erosion aredynamically moved toward the target cylinder ends to achieve an overalltarget utilization that is improved relative to the prior art. Higherpercentage target utilization as a weight percentage is achievedcompared to the prior art. The expense and effort associated withdog-boned target cylinders is also precluded.

A longitudinal cross sectional view of the present invention is shown inFIG. 4 and depicts the target cylinder 1 and the inventive stationarymagnet bar shown generally at 200 and underlying the turnaround region 3of rotary magnetron racetrack 2 that generates plasma during operation.Like numerals in this figure have the meanings ascribed thereto withrespect to the preceding figures. Starting with a conventional rotatingtube cylinder 1 having a backing tube 14 with target material 10 formedaround the backing tube 14. The target surface 15 indicates the startingouter diameter of target tube cylinder 1 with target material 10 maximalextent prior to sputtering. The stationary magnet bar shown generally at290 has a shunt 206 and magnets 208, 207 and magnet 230. The magnet bar290 extends to the right as indicated by multiple magnets denotedgenerally at 208′ and underlie straight portions 4 of the racetrack 2.While the magnet bar 290 is depicted as a single row of magnets, it isappreciated that the present invention is also operative with multiplerows of magnets, as for example depicted in FIG. 2 of U.S. Pat. No.5,364,518.

According to the present invention, the erosion zone 214 is shiftedoutward towards the end 232 of target tube 1 with the removal of targetmaterial 10. This results in the erosion zone 214 being dynamicallydisplaced into the comparatively thicker, target tube end section 232.This is in contrast to the prior art continued wear at the maximal wearregion of cylinder section 13 of FIGS. 1 and 2. Through the lateral andangular dynamic shift in the erosion zone 214, overall targetutilization is improved compared to the prior art. Target utilizationaccording to the present invention is measured to exceed 70%, 75%, 80%,85%, and as much as 87% of the initial weight of the target material 10.This compares to approximately 60% of the initial weight of the targetmaterial 10 being usable for conventional systems including that of U.S.Pat. No. 5,364,518. Aluminum and aluminum alloys are merelyrepresentative of target materials 10 from which a target cylinder 1 isformed.

Dynamic shifting of the erosion zone 214 is accomplished with theconfiguration of magnets: distal magnet 207, proximal magnet 208 andintermediate magnet 230. The magnets 207, 208, 208′, and 230 are eachindependently a bar magnet, or an electromagnet. The placement of anintermediate magnet 230 pulls field lines from distal magnet 207 andcauses the magnetic field apex line 209 to shift away from normal line231 by angle θ, also referenced with numeral 210 as the target material10 is removed by plasma sputtering. It is appreciated that placement ofintermediate magnet 230 spaced apart synonymously, referred to asnon-contiguous with magnets 207 or 208 affords certain advantages inadjusting magnetic field lines extending through the target material.The placement of intermediate magnet 230 distal of the interior edge 5of turnaround portion 3 is preferred to shift the erosion zone towardthe tube end, as shown in FIG. 4. According to the present invention,the angle θ dynamically changes from 0 at line 231 through an angle θ ofup to 70 degrees, as measured the direction orthogonal to the lowestpoint of erosion at profile 202. Factors relevant in achieving the valueof θ at terminal profile 202 include the thickness and identity oftarget cylinder 1, magnetic strength and relative spacing of magnets207, 230, 208, and 208′, magnetic permeability of target material 10,and relative dimensions and operating conditions for the racetrack 2. Atypical 1 meter long aluminum taget cylinder used under industrialdeposition conditions has θ values that shift between 0 and 50 degreeswhile the erosion zone for such a target typically shifts toward end 232from 0.5 to 5 centimeters.

As the apex line 209 moves closer to the end 232 of target tube 10, asthe target material 10 is removed by sputtering, the result of thismagnetic field configuration is shown in the series of dynamicsuccessive erosion profiles 211, 212, 213 and 202. Initially, themagnetic field apex 209 is positioned over the original target surface15 and results in the erosion zone at 233. As the target tube erodes,the apex shifts toward the end 232 of the target cylinder 1 andconsequently the target erosion zone 214 also moves toward the end 232of the target cylinder 1. As is shown, as the apex line shifts, theerosion zone moves onto the side of the target tube 232. This slows theerosion at the bottom of the target and extends target utilizationpercentage and therefore operational lifetime.

FIG. 5A shows a comparison of rotary target wear between the prior artand the present invention. The prior art wear profile is shown as adashed line 13 corresponding to region 13 of FIG. 1B. Minimal point 7 isthe prior art wear point underlying the turnaround portion 3 that causespremature target end of life. The deep wear at 7 leaves unusablematerial 12 underlying the straight portion 4 of the plasma generatorracetrack 2 extending linearly to the right as depicted in FIG. 5A andparallel above the backing tube 14. In the present invention, a superiormaterial utilization wear profile achieved. At the end of the targetlife, the straight away material 202 is worn down almost to backing tube14. The end 232 forms a flange intersection with the adjacent erosionzone 202 and at an angle β of greater than 50, 55, 60, 65, 70, 75, 80,85 and almost 90 degrees at the end of an operable lifetime for thetarget cylinder 1. The angle β is measured by extrapolating theintersection of a line orthogonal to the surface 15 and from the erosionzone 202 less the angle γ between end 232 and the orthogonal line suchthat β+γ=90 degrees. At the target region underlying the racetrackturnaround portion 3 and well into target usage, the target tube sidewall 232 is eroded almost perpendicular to the original tube surface 15.

It is appreciated that greater tube utilization is achieved by a numberof magnet configurations. The intermediate magnet is positioned at angleα that has the north polar orientation within 10 degrees of that ofproximal magnet 208 (80-110 degrees) or within 10 degrees of orthogonalto both the distal magnet 207 and the proximal magnet 208 (170-190 or10-350 degrees). With these angular orientations being based on magnet207 defining and angle of 270 degrees as shown and magnet 208 defining90 degrees in a plane projecting orthogonal to the plane of the page.For instance, magnet 230 can be laid orthogonal to the position depictedin FIG. 4 on its side with the pole arrow projecting into (0 degrees) oroutward of the page plane (180 degrees) so as to be perpendicular tomagnet 207 with the angle defined by α in FIG. 4. These alternateorientations are shown in displaced position as 230A and 230B,respectively. It is appreciated that magnets 207 and 208 each isindependently and optionally shaped or stacked. A shaped magnetic isdefined herein as one that deviates from a rectilinear cuboid. It isappreciated that magnet face shaping proximal to the tube backing 14 isparticularly helpful in controlling magnet field shape and strength. Astacked magnet is defined herein as a magnet that is not monolithic andinstead formed by combining several distinct magnetic elements in anadditive manner.

FIG. 5B shows an overlay of the fitting functions onto the normalizedterminal erosion zone cross sections of the prior art of FIG. 2C andpresent invention of FIG. 5A. The best two parameter fit of Equation Ito the inventive erosion zone profile occurs with D_(f)=0.075, k=1 andl_(f)=1.51, as shown in FIG. 5B.This erosion profile is also readilymodeled with a step function, with the location of the step beingreadily modeled based on a magnetic field line simulation for theinventive magnet bar underlying the target cylinder, as shown forexample in FIG. 4. A two parameter best fit extending for ten units oflength, l and a normalized thickness of unity for an inventive erosionprofile has values for D_(f) of between 0.01 and 0.3 and l_(f) ofgreater than 1 and in particular between 1.1 and 2.0.

Any patents or publications mentioned in this specification areindicative of the levels of those skilled in the art to which theinvention pertains. These patents and publications are hereinincorporated by reference to the same extent as if each individualpublication was specifically and individually indicated to beincorporated by reference.

One skilled in the art will readily appreciate that the presentinvention is well adapted to carry out the objects and obtain the endsand advantages mentioned, as well as those inherent therein. The presentmethods, procedures, treatments, molecules, and specific compoundsdescribed herein are presently representative of preferred embodiments,are exemplary, and are not intended as limitations on the scope of theinvention. Changes therein and other uses will occur to those skilled inthe art which are encompassed within the spirit of the invention asdefined by the scope of the claims.

We claim: 1.-9. (canceled)
 10. A process of coating a substratecomprising: energizing a tubular target formed of a tube material andhaving a tube end affixed to a tubular cathode under conditions togenerate a sputtering racetrack-shaped plasma extending towards thesubstrate; arranging a plurality of magnets inside said cathode to forma magnetic field which interacts with a racetrack-shaped plasma sourcealigned with said target, said plasma source having two straightportions and at least one terminal turnaround portion connecting saidstraight portions to move an erosion zone on said tubular target alignedwith at the least one terminal turnaround toward the end of said targetas said target is utilized to deposit the coating on the substrate. 11.The process of claim 10 wherein said erosion zone shifts toward the endas said target is sputtered and away from said straight portions. 12.The process of claim 10 wherein said erosion zone shifts away from anormal line to a target initial surface by an angle θ of up to 70degrees.
 13. The process of claim 10 wherein said target is utilized tobetween 70 and 87 weight percent the target material.
 14. The process ofclaim 10 wherein a portion of said target defining said end forms aflange intersection at said erosion zone at an angle β of between 70 and90 degrees at a termination of an operable lifetime for said target.15.-20. (canceled)
 21. A method for efficient target utilization forrotary magnetron sputtering comprising: a) assembling one or more rotarymagnetron plasma sources comprising one or more targets formed of a tubematerial and having a tube end and is affixed to one or more tubularcathodes that forms the tube backing, placing magnets inside the one ormore tubular cathodes to create magnetic fields; b) placing one or morerotary magnetron plasma sources in a vacuum chamber; c) placing asubstrate in a vacuum chamber adjacent to the one or more rotarymagnetron plasma sources; d) energizing the one or more rotary magnetronplasma sources to initiate racetrack plasmas adjacent to the targetswhere the magnets inside the cathodes of the one or more rotarymagnetron plasma sources create magnetic fields which interacts with theracetrack plasmas to move the erosion zone on the tubular target of theone or more rotary magnetron plasma sources toward the end of the targetas the target is utilized; and e) operating the one or more rotarymagnetron plasma sources until 61-90% of the initial target weight iseroded.